The ear canal 10, as illustrated in FIG. 1, is generally narrow and tortuous and is approximately 26 millimeters (mm) long from the canal aperture 11 to the tympanic membrane 15 (eardrum). The lateral part 12 is referred to as the cartilaginous region due to the underlying cartilaginous tissue 16 beneath the skin. The medial part, proximal to the tympanic membrane 15, is rigid and referred to as the bony region 13 due to the underlying bone tissue 17. A characteristic first bend occurs roughly at the aperture 11 of the ear canal. A second characteristic bend occurs roughly at the bony-cartilaginous junction 8 and separates the cartilaginous region 12 and the bony region 13. The ear canal 10 is generally hidden from view (front and side) behind a backward projecting eminence known as the tragus 3. The ear canal is also hidden from view from the back by the presence of the pinna 4 (also referred to as auricle). The dimensions and contours of the ear canal 10 vary significantly among individuals.
Placement of a hearing device inside the ear canal 10 is generally desirable for various electroacoustic advantages such as reduction of the acoustic occlusion effect, improved energy efficiency, reduced distortion, reduced receiver vibrations, and improved high frequency response. Canal placement may also be desirable for cosmetic reasons since the majority of the hearing impaired may prefer to wear an inconspicuous hearing device. A canal hearing device can be inserted entirely or partially inside the ear canal. In the context of this application, any hearing device inserted inside the ear canal, whether partially or completely, may be referred to as a canal hearing device. This includes what is known in the hearing aid industry as Completely In the Canal (CIC), In-The-Canal (ITC), and extended wear deep canal invisible types.
Conventional batteries for canal hearing devices include zinc-air varieties, which are generally non-rechargeable, thus replaced frequently by the user. Given the advanced age of the average hearing aid user and diminutive size of canal hearing device batteries, it is an inconvenient and often a frustrating task to replace the batteries due to decreased dexterity and impaired vision. Furthermore, standard zinc-air batteries can drain prematurely due to continuous internal discharge after removing the air-access tab as known in the hearing aid field. Rechargeable hearing aids on the market are generally limited to the relatively unsightly larger devices in the form of Behind-The-Ear (BTE), In-The-Ear, and Receiver-In-The-Canal (RIC), which are typically made sufficiently large to accommodate charging mechanisms, without the need to remove the battery cell within during charging.